A typical hypodermic syringe has a hollow needle at one end of a cylindrical fluid container and a moveable plunger at the opposite end of the fluid container. The plunger is used to discharge fluid from the fluid container through the needle, or to draw fluid through the needle into the cylindrical fluid container. In order that the needle enter painlessly into the skin, the needle tip usually has a small cross-sectional area and is extremely sharp. Because of the sharpness of the syringe needle, use of the syringe requires great care, since even the most casual contact of the needle with the skin is likely to penetrate the skin, a circumstance commonly known as a "needle stick". The term "needle stick" as used herein, refers to an unintentional or accidental penetration of the skin by a hypodermic syringe needle.
Although a needle stick is a minor injury, it carries the threat of transmitting such diseases as hepatitis and AIDS. Additionally, undesired drugs or toxins may be accidentally transmitted by a needle stick. In order to alleviate the problems of needle stick, a removable protective sheath or cap, is installed over the needle. The protective sheath is an elongated sleeve which is slightly longer than the needle. The sheath is closed at one end and has an opposite end that pressfits onto the base of the needle support structure of the syringe. The sheath is relatively narrow and protects the needle while permitting safe handing of the syringe when the syringe is not in use.
Before using the syringe, the protective sheath must be removed from the needle, a procedure known as uncapping. During uncapping, the sheath is normally gripped between the fingers of one hand, while the other hand holds the cylinder or main body portion of the syringe. Any contact between the needle tip and the hand during the uncapping process can cause a needle stick.
After the syringe has been used, the protective sheath is often replaced over the needle, a procedure known as recapping. During recapping, the protective sheath is again held in one hand and the main body of the syringe is held in the other hand. Any shake of the hand and any misalignment of the needle and sheath during recapping is likely to result in a needle stick to the hand which holds the sheath. Therefore, the problem of needle sticks during recapping is significant.
A need has thus arisen for a safety device for preventing needle stick during uncapping and recapping of a needle of a hypodermic syringe. Such a safety device must be easy to use and fast in operation while providing protection to the user against needle stick.